The present invention relates to a polishing apparatus, and more particularly, to a polishing apparatus adapted so as to detect a failure during polishing a substrate such as a semiconductor wafer or the like. The failure can include a breakage of the wafer or an event of the wafer jumping from a predetermined position, which may occur during polishing the substrate.
In recent years semiconductor devices have become so highly integrated that circuit interconnections have become thinner and that distances between these interconnections have also become smaller. Particularly, for an optical lithography of 0.5 xcexcm or less, the depth of focus has become so short that a high degree of flatness on an imaging surface of an exposure apparatus is required. Hitherto, a self-flattening CVD apparatus or an etching apparatus has been used as a flattening apparatus for flattening a semiconductor wafer. These apparatuses, however, do not accomplish a sufficient degree of flatness. Therefore, a polishing apparatus has recently been extensively adopted to flatten a semiconductor wafer because a higher degree of flatness can be expected to be accomplished more readily than the flattening apparatuses described immediately above.
The polishing apparatus of this type is composed of a turntable and a top ring member, each rotating at a number of rotations discretely and independently from each other, and an abrasive cloth is attached on top of the turntable. Between the turntable and the top ring member is interposed a substrate (e.g., a semiconductor wafer), and the substrate is pressed against a top surface of the abrasive cloth at a predetermined pressure. The surface of the substrate is then polished to a predetermined level of flatness and to a mirror surface while a polishing fluid is being fed thereto. After the completion of the polishing process, the substrate is detached from the top ring member and subjected to post-processing processes, including a cleaning process.
It is to be noted herein; however, that the substrate may break and broken pieces may scatter on the abrasive cloth during the polishing process. Damage to the surface of a new substrate results if the abrasive cloth is used again. Therefore, a new abrasive cloth has to be used whenever a substrate breaks. On the other hand, even if a substrate is not broken into pieces, a failure of the substrate may result, for instance, when the substrate jumps from the top ring member during the polishing process. If the substrate is a semiconductor silicone wafer or the like made of a brittle material and the substrate jumps from the top ring member, the substrate may be damaged or chipped at its outer peripheral portion due to impact with a wall surface or the like of the turntable. The damaged substrate is very likely to be broken by application of a slight force onto the damaged portion or at a position close to the damaged portion, when the damaged substrate is polished again.
In order to solve the problems as described above, proposals to prevent a failure while polishing, including a breakage or jump of a substrate from the top ring member, have been devised. For instance, there has been proposed a process for reducing an occurrence of breaking or chipping of a substrate upon polishing the substrate by using a polishing apparatus with a buffer member such as an elastic mat interposed between a bottom surface of the top ring member and the substrate. Alternatively, there has been proposed a process whereby a jump of a substrate is prevented by fixing the substrate within the top ring member while guiding an outer periphery of the substrate.
These proposals, however, are concerned with precautionary measures to prevent a breakage of jump of the substrate, and are useless to deal with an event once the substrate is broken or has jumped outside the top ring member. To deal with an event of a substrate jumping from the top ring member, there has hitherto been adopted a process for immediately suspending a polishing operation of a polishing apparatus as a detection system detects a jump of the substrate outside the top ring member. The detection system is devised to detect the jumping of the substrate from the top ring member and is disposed outside the top ring member.
This process, however, suffers from a problem in that the polishing operation cannot be suspended rapidly because the jumping of the substrate can only be detected after the substrate has already jumped, with the result that the timing of detection is delayed.
Moreover, this process has another problem in that a failure upon polishing caused by a breakage of the substrate cannot be detected. As a result, there is a risk that the polishing of the substrate is continued unless the broken substrate jumps from the top ring member.
Therefore, the present invention has been completed under circumstances as described above and has as an object to provide a polishing apparatus that can prevent an occurrence of damages due to a failure while polishing a substrate, including a breakage or a jump of the substrate, by continually managing polishing operations of the substrate during the polishing process.
In order to achieve the object, one aspect of the present invention provides a polishing apparatus comprising a polishing tool and a substrate holding member to hold a substrate and press a surface of the substrate against the polishing tool. The polishing tool and the substrate holding member are arranged so as to more relatively to each other to polish the substrate. A sensor is disposed outside the substrate holding member for sensing a distance between the sensor and a surface of the polishing tool. And, a control unit is disposed to determine an occurrence of a failure while polishing the substrate, including a breakage or jump thereof from the substrate holding member, on the basis of a variation in the distance measured by the sensor caused by an intervention of the substrate above the surface of the polishing tool.
In another aspect, the polishing apparatus according to the present invention comprises a polishing tool and a substrate holding member to hold a substrate and press a surface of the substrate against the polishing tool. The polishing tool and the substrate holding member are arranged so as to move relatively to each other to polish the substrate. A failure detection sensor to detect a polishing failure while polishing the substrate, including a breakage or jump of the substrate, is disposed within or above the substrate holding members so as to detect such a polishing failure prior to a jump of the substrate from the substrate holding member.
In preferred embodiments of this aspect of the present invention, the failure detection sensor may include a supersonic sensor, a displacement sensor, a piezoelectric element, a distortion sensor or a vibration sensor.
In a further aspect of the present invention, the polishing apparatus comprises a polishing tool and a substrate holding member to hold a substrate and press a surface of the substrate against the polishing tool. The polishing tool and the substrate holding member are arranged so as to move relatively to each other to polish the substrate. A condenser is composed of electrode plates disposed so as to hold therebetween both faces of the substrate held by the substrate holding member, or electrode plates disposed so as to sandwich the substrate which has jumped outside the substrate holding member. A electric power source is disposed to apply a predetermined constant voltage to the condenser, and an ammeter is disposed to measure a current passing through the condenser, whereby a polishing failure during polishing, including breakage or a jump of the substrate, is detected.
In a still further aspect of the present invention, the polishing apparatus comprises a polishing tool and a substrate holding member to hold a substrate and press a surface of the substrate against the polishing tool. The polishing tool and the substrate holding member are arranged so that they move relatively to each other to polish the substrate. A contact member is disposed in contact with a bottom face of the substrate holding member or with the polishing tool at its periphery. And, a measuring system is disposed to allow a current to flow between the contact member and a surface of the polishing tool and to measure a current value therebetween, whereby a failure during polishing, including breakage or a jump of the substrate from the substrate holding member, is detected on the basis of a variation in the current value caused by the substrate passing between the contact member and the surface of the polishing tool.
In a still further aspect of the present invention, the polishing apparatus comprises a polishing table and a substrate holding member to hold a substrate and press a surface of the substrate against the polishing tool. The polishing tool and the substrate holding member are arranged so that they more relatively to each other to polish the substrate. A measuring device is disposed to measure a drive current of a drive unit for driving at least one of the polishing tool and the substrate holding member. And, a failure detection unit is disposed to detect a polishing failure while polishing the substrate, including breakage or a jump of the substrate from the substrate holding member, on the basis of a comparison of the drive current during polishing with a threshold value, or a comparison of a waveform pattern of the drive current at the time of causing the polishing failure.